Water jet propulsion system

ABSTRACT

A highly efficient watercraft propulsion system that relies on a positive displacement pump to generate a water jet. The pump is fully submerged at all times and its inlet is positioned so as to cause water to be forced into the pump as the watercraft moves through the water. The pump is preferably combined with a variable area pump opening which is configured, positioned and oriented so as to maximize the hydraulic reaction between the water jet stream and the surrounding body of water.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 11/771,035,filed on Jun. 29, 2007, which is a divisional of U.S. Ser. No.11/103,318 filed on Apr. 11, 2005, now U.S. Pat. No. 7,238,067.

BACKGROUND

The present invention generally relates to water jet propulsion systemsfor watercraft and more particularly pertains to the use of a particulartype of pump configuration and its adaptation to a watercraft to achieveenhanced efficiency.

A variety of jet pump configurations have previously been used to propelwatercraft. Most such configurations comprise kinetic pumps of one formor another that serve to accelerate water to a high velocity in order toachieve the desired propulsive force. The losses associated with thehigh velocities, the non-aligned flow and the turbulent flow inherent inthe operation of many such pump configurations limits the efficiencythat is ultimately attainable. Nonetheless, kinetic pumps, or dynamicpumps as they may also be referred to, are the most commonly used typeof pump for marine propulsion applications and typically rely on animpeller to push water through a duct. Positive displacement pumps onthe other hand are capable of generating high hydrostatic pressures atessentially zero velocity and could conceivably be able to providesubstantial gains in terms of efficiency. However, the positivedisplacement pump configurations that have been proposed for thepropulsion of watercraft and the adaptations of such pumps to watercraftthat have been proposed have failed to cause the use of positivedisplacement pumps to gain wide acceptance for such purpose.

It is well known that the velocity with which a water jet is dischargedfrom a watercraft relative to the velocity of the watercraft has adirect effect on the efficiency of such a system. Propulsion efficiency,whether measured with respect to fuel consumption or vessel speed, is afunction of both water jet discharge velocity and volumetric flow. Whilethe water jet discharge velocity can of course be controlled by pump'svolumetric output, the jet velocity can also be controlled by varyingthe cross-sectional area of the orifice through which the water isdischarged. Accordingly an increase in the cross sectional area of thedischarge orifice for a given pump output reduces the water dischargevelocity while a decrease of the cross-sectional area serves to increasesaid velocity.

It has long been recognized that the ability to vary discharge orificearea can significantly enhance propulsion efficiency over a wide rangeof operating conditions and thereby reduce fuel consumption. A largevariety of configurations that are either cylindrical, conical,hemispherical or combination of same have been suggested for a dischargeorifice that is variable in terms of both area and flow path shape alongwith various mechanisms to control the water discharge velocity as afunction of any of various parameters. Even greater efficiency wouldnonetheless be desirable.

SUMMARY OF THE INVENTION

The present invention provides a highly efficient water jet propulsionsystem for a watercraft by relying on a non-pulsating positivedisplacement pump to move water through a duct. Moreover, the pump ispreferably arranged so as to be fully submerged at all times. It isfurther preferred to arrange its inlet opening such that water is forceddirectly into the pump by the movement of the watercraft through thewater. It is additionally preferred to combine the pump with a submergedvariable area discharge opening so as to allow for the velocity of thedischarge jet to be optimized relative to the velocity of thesurrounding water. Finally, it is preferred to package the entirepropulsion system so as to be attachable to the bottom of a hull orother fully submerged surface of a watercraft.

A positive displacement pump displaces a preselected volume of waterfrom the input side of the pump to the output side of the pump with eachpump cycle or rotation and substantially precludes any return of waterfrom its output side to its input side even when operating at lowvelocities and/or under high head pressures. Positive displacement pumpsadd both potential energy as well as kinetic energy to a continuallydisplaced volume of water and the displaced volume per cycle or rotationis independent of cycle or rotation rate. As such, positive displacementpumps are readily distinguishable from kinetic or dynamic pumps thatrely on for example impellers or paddle wheels to move water. A positivedisplacement pump is capable of generating substantial hydrostaticpressures at very low jet velocities. Non-pulsating configurationsgenerate a constant flow throughout each cycle or rotation. Thisdelivery characteristic has unexpectedly been found to further enhanceefficiency in propelling a watercraft. The net result is an increase inperformance potential, a reduction in fuel consumption and acommensurate reduction in emissions.

The preferred pump configuration is a counter-rotating rotor pump whichmay also be referred to as a counter-rotating lobe pump or external gearpump. Additionally it is preferred that the rotors' lobes follow ahelical path along the rotors' rotational axes with a sufficient amountof twist to ensure that there is a continual discharge of fluid as therotors are rotated. An example of such a pump is described in U.S. Pat.No. 3,164,099 to Hitosi Iyoi which is incorporated herein by referencein its entirety.

The efficiency provided by the positive displacement pump is furtherenhanced with its combination with a discharge opening that iscontinuously variable in terms of its cross-sectional area. Suchdischarge configuration employs an opening having a cross-sectionalshape that is substantially trapezoidal. The sides of the dischargeopening transverse to the parallel sides are straight or curved and maybe substantially parallel so as to define a rectangle. Additionally, thedischarge duct is positioned on the submerged portion of the watercrafthull so that the pump discharge flow is ejected into the surroundingwater thereby creating a direct hydraulic coupling to thereby enhancethrust efficiency.

It is additionally preferred that the inlet be arranged so as to causewater to be forced into the pump as the watercraft moves through water.This inlet ram feature has the benefit of increasing the static pressurehead on the suction side of the pump thereby reducing the possibility ofrotor cavitation at high pump speeds and therefore allows the pump tooperate at higher speeds than have heretofore been possible. Efficiencyis further enhanced by arranging the inlet, pump and outlet along astraight line. This not only ensures that the entire propulsion systemis fully submerged at all times to preclude any loss of prime butfurther eliminates any inefficiencies that could otherwise be introducedif the flow of water into, through and out of the pump were forced tochange direction.

On vessels that generally have a flat bottom, the discharge opening ofthe duct may generally define a horizontally oriented taperedtrapezoidal duct. On large vessels, several ducts may be installed atvarious orientations on the submerged portion of the curved hull. Acontoured or generally wedge-shaped control element is movably disposedwithin the duct such that its narrow end is variably extendible outthrough the exit of the discharge opening. The control element therebyserves to block off a central portion of the discharge opening to reducethe total cross-sectional area that remains open to the flow of waterthere through. Its wedge shape serves to block off a progressivelylarger portion of the discharge opening's cross-sectional area as thecontrol element is caused to translate out through the discharge openingwhich in turn results in an increase in the water jet velocity.Conversely, retraction of the control element serves to increasecross-sectional area to thereby reduce water jet velocity.

The linear position of the wedge-shaped control element may betranslated by any number of actuation means including, but not limitedto, mechanical, hydraulic, or servo electronic systems or combinationsthereof. A variety of different control means may also be relied upon togovern the position to which the control element is actually shiftedincluding, but not limited to, manual selection, direct action of pumpoutput or more sophisticated systems such as for example amicroprocessor that considers a plurality of parameters and calculatesan optimum setting. A preferred embodiment simply relies on the actionof a spring to bias the control member into its retracted position. Asthe force of the flow of water impinging on the frontal surfaces of thecontrol element is increased by an increase in the volumetric pumpoutput, the bias of the spring is overcome to cause the control element,which is constrained vertically between the upper and lower, parallelsurfaces of the discharge duct, to shift linearly towards the dischargeopening thereby causing a further increase in flow velocity.

The location and orientation of the discharge opening serves to furtherenhance the propulsion efficiency of the water jet discharge system ofthe present invention. Accordingly, the discharge opening is positionedso as to remain submerged at all times to create a direct hydraulicreaction between the discharge jet and the surrounding body of water. Bypositioning the discharge opening so as to extend from the bottom of thehull at a location substantially forward of the trailing edge of thehull, the section of hull aft of the discharge opening in the plane ofthe upper surface of the duct prevents the upward diffusion of the jet.Additionally, an extension of the duct's bottom surface aft of thedischarge opening limits the amount of downward diffusion of the jet inthe plane of the lower surface of the duct. By constraining thedischarged jet between the hull and the duct extension aft of thedischarge opening, a greater portion of the discharge flow isconstrained so as to remain substantially parallel to the direction ofdesired thrust i.e. in-line with the direction of travel. The result isan increase in axial thrust, or vessel driving force, than if the pumpdischarge is allowed to diffuse freely.

The pump, inlet opening and discharge opening are preferably disposedwithin a housing that is attachable to the bottom of the hull of awatercraft. A transfer box extending upwardly and through the hull isrelied upon to transfer rotation from a prime mover to the pump. It isimportant that the shape of the submerged portion of the pump housing isstreamlined in such a way so as to minimize the hydrodynamic impact ofits presence in such a critical location.

These and other advantages of the present invention will become apparentfrom the following detailed description of preferred embodiments which,taken in conjunction with drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a watercraft fitted with the propulsion systemof the present invention;

FIG. 2 is a front view of the watercraft shown in FIG. 1;

FIG. 3 is a rear view of the watercraft shown in FIG. 1;

FIG. 4 is a perspective view of the submerged portion of the housingthat contains the propulsion system of the present invention;

FIG. 5 is a sectioned perspective view taken along lines V-V of FIG. 1;

FIG. 5 a is a perspective view of the helical rotors shown in FIG. 5;

FIG. 6 is a cross-sectional view of an alternative embodiment ofdischarge opening configuration of the propulsion system of the presentinvention shown in its full retracted state;

FIG. 7 is a cross-sectional view of the discharge opening configurationshown in FIG. 6 in its fully protracted state;

FIG. 8 is a cross-sectional view of an alternative embodiment of thepropulsion system of the present invention;

FIG. 9 is a perspective view of a preferred embodiment of the propulsionsystem of the present invention; and

FIG. 10 is a cross-sectional view of the propulsion system shown in FIG.9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The water jet propulsion system of the present invention provides forenhanced efficiency in the propulsion of a watercraft. The figuresgenerally illustrate preferred embodiments of the propulsion system interms of its pump configuration, its adaptation to and orientationrelative to a hull, a mechanism for varying the cross-sectional area ofthe discharge opening and the packaging of its various components.

FIG. 1 is a side view of a watercraft 12 showing the propulsion system14 of the present invention fitted to the bottom of its hull 16. Thesystem includes a housing 18 that contains a pump (not visible) and hasan inlet opening 20 at its forward end and a discharge opening 22 at itsaft end. The housing is positioned under the hull so as to ensure thatthe inlet opening, pump and discharge opening remain fully submerged atall times during all modes of operation. The submersion of the outletopening even under maximum acceleration from low speeds or at maximumvelocity ensures that the hydraulic reaction between the liquid jetstream and the adjacent, relatively static body of water can bemaximized at all times. As can be seen in the FIG. 1, the dischargeopening is positioned well forward of the aft edge 24 of the hull.

FIG. 2 is a front view of the watercraft 12 showing the propulsionsystem 14 extending below the hull 16. The inlet opening 20 is showncentered in the forward end of the housing 18. FIG. 3 is a rear view ofthe watercraft 12 showing the propulsion system 14 extending below thehull 16. The outlet opening 22 is shown centered in the aft end of thehousing 18. FIG. 4 is a perspective view of the submerged portion of thehousing 18 that contains the propulsion system 14 disposed on the bottomof the hull 16.

FIG. 5 is a perspective view of a cross-section of the propulsion system14 taken along lines V-V of FIG. 1. Visible in this view is jet pump 26that is substantially centrally located within housing 18. The preferredpump configuration that is shown is a counter-rotating helical rotorpump. In the preferred embodiment shown, each rotor 28, 30 includesthree lobes 32, wherein the rotors are positioned such that the lobesfrom each rotor sealingly intermesh with one another at the center andsealingly engage the seal regions 34 that are formed in each side of thehousing. Rotation of the rotors causes a fluid to be positivelydisplaced from one end of the pump to the opposite end of the pump whilebackflow is precluded. Rotation in the direction indicated by the arrowswill cause fluid to be forced from the inlet end 20 to the outlet end22. Only one particular such pump configuration is shown while differentnumbers of lobes and lobe profiles can be used. In the preferredembodiment, the lobes 32 and hence the recess 36 there between describea helical shape relative to the axis of rotation 38 of each rotor as ismost visible in FIG. 5 a. The number of lobes and recesses willdetermine the angle that is described by the seal regions 34.Additionally shown in FIG. 5 are gussets 42, 44 that are position withinboth the inlet end 20 as well as the outlet end 24 of the housing 18.The gussets serve not only to align the flow to and from the pump butalso serve as structural members to reinforce the housing.

While the embodiment illustrated in FIG. 5 has a discharge opening witha fixed cross-sectional area, further efficiencies are gained with thefitment of a mechanism for varying the cross-sectional area of thedischarge opening such as is shown in FIGS. 6 and 7. A moveable controlelement 46 is positioned in the discharge opening 22 and is shaped suchthat a shift in its longitudinal position will cause the discharge area48 to change. Full retraction of the control member, as is shown in FIG.6, will serve to maximize the cross-sectional area and thereby minimizethe velocity of the flow of water while full protrusion, as is shown inFIG. 7, will minimize the cross-sectional area and thereby maximize thevelocity of the flow of water. Any of a variety of control memberconfigurations can be employed as can any of various mechanisms to alterthe position of the control member so as to achieve a desirable ratio ofthe jet velocity relative to the surrounding water velocity. FIG. 8illustrates an alternative preferred embodiment wherein five lobehelical rotors 28 a, 30 a force the flow of water past two controlelements 46 a, 46 b. Additionally visible is a bottom lip 50 a thatextends beyond the discharge opening from the bottom surface of thehousing to limit downward diffusion of the water jet.

FIG. 9 is a perspective view of the propulsion system 14 of the presentinvention. A transfer box 52 extends from the top of the housing 18 fortransferring rotation from a prime mover (not shown) via flange 54 tothe pump rotors that are disposed within the housing. Both the inletopening 20 as well as the discharge opening 22 are visible. A flange 56extends about the periphery of the housing to facilitate its attachmentto the bottom of a hull. Any of a variety of prime movers can be reliedupon to power the propulsion system including, but not limited tointernal combustion engines, electric motors, hydraulic motors, verticalaxis wind turbines and even human power.

FIG. 10 is a cross-sectional view of the embodiment shown in FIG. 9. Inthis particular embodiment, a flow 58 of water into the inlet opening20, past rotor 30 and out through discharge opening 22 can describe asubstantially horizontal path. The decrease in the height of the outletconduit and the commensurate decrease in cross-sectional area serves toaccelerate the jet before being discharged. In the particular embodimentthat is illustrated, a gear set 60, 61 serves to transfer rotation fromflange 54 to the rotors.

In operation, reliance on a non-pulsating positive displacement pump inwater jet propulsion systems yields substantial gains in efficiency overpreviously used devices. More specifically, a counter-rotating helicalrotor pump is able to provide an aligned continuous flow at the mostefficient velocity without turbulence. The non-pulsating flowcharacteristic eliminates the thrust disruptions inherent in pulsatingconfigurations and the inefficiencies resulting therefrom. Such pump inconjunction with a fully submerged discharge opening having a variablecross-sectional area yields extremely high propulsion efficiency overthe entire range of pumping capacity. Adjustment of the cross-sectionalarea of the discharge opening allows the discharge jet velocity to beset to propel a vessel at its best fuel efficiency or, if desired, toprovide maximum driving force over a wide range of vessel operatingparameters such as weight, displacement and weather conditions. Thesubmerged variable area discharge opening in combination with theinstallation location on the hull and a bottom lip serve to limitdiffusion of the water jet thereby minimizing the dynamic mixing lossesaft of the discharge plane allowing the hydraulic reaction to bemaximized. It is contemplated that the propulsion system of the presentinvention can be sized and adapted to most any watercraft from motorizedsurfboards and kayaks, to sport and pleasure boats to freighters andtankers. In each such application, overall energy consumption can besignificantly reduced as the water discharge velocity leaving thehousing can be optimized at any given vessel speed to yield the highestpossible propulsion efficiency using the least amount of fuel. Unlikewater jet propulsion systems that discharge above the waterline of avessel, there is no need for complicated diversion systems that directthe flow of water forward to provide reverse thrust. A simple reversingof the rotor rotation provides reverse thrust by causing the water toflow from the submerged discharge end out the submerged inlet.

While particular forms of the invention have been described andillustrated, it will also be apparent to those skilled in the art thatvarious modifications can be made without departing from the spirit andscope of the invention. Accordingly, it is not intended that theinvention be limited except by the appended claims.

1. A water jet propulsion system for a watercraft, comprising a non-pulsating positive displacement pump.
 2. The water jet propulsion system of claim 1, wherein said non-pulsating positive displacement pump comprises a counter-rotating helical lobe pump.
 3. The water jet propulsion system of claim 1, further comprising an inlet opening, a discharge opening and wherein said inlet opening, discharge opening and pump are arranged in a straight line.
 4. The water jet propulsion system of claim 1, further comprising an inlet opening, a discharge opening and wherein said inlet opening, discharge opening and pump are fully submerged at all times.
 5. The water jet propulsion system of claim 4, further comprising a variable area discharge opening.
 6. The water jet propulsion system of claim 5, wherein said watercraft includes a hull and wherein said discharge opening is positioned such that a discharged jet of water flows along a submerged portion of said hull.
 7. The water jet propulsion system of claim 4, wherein said inlet opening is positioned so as to cause water to be forced directly into said pump when said watercraft is moving through said water.
 8. A water jet propulsion system for a watercraft, comprising a counter-rotating lobe pump.
 9. The water jet propulsion system of claim 8, wherein said lobes have a helical shape extending along their axes of rotation.
 10. The water jet propulsion system of claim 8, further comprising an inlet opening, a discharge opening and wherein said inlet opening, discharge opening and pump are arranged along a common axis.
 11. The water jet propulsion system of claim 8, further comprising an inlet opening, a discharge opening and wherein said inlet opening, discharge opening and pump are fully submerged at all times.
 12. The water jet propulsion system of claim 11, further comprising a variable area discharge opening.
 13. The water jet propulsion system of claim 11, wherein said watercraft includes a hull and wherein said discharge opening is positioned such that a discharged jet of water flows along a submerged portion of said hull.
 14. The water jet propulsion system of claim 8, wherein said inlet opening is positioned so as to cause water to be forced directly into said pump when said watercraft is moving through said water.
 15. A water jet propulsion system for a watercraft having a hull, comprising: a counter-rotating helical lobe pump; an inlet conduit for conducting water directly into said pump; an outlet opening for conducting water discharged water from said pump; a housing for said pump, inlet conduit and outlet orifice, wherein said housing is configured for attachment to said hull.
 16. The water jet propulsion system of claim 15, further comprising a power transfer box for transferring rotation from a prime mover to said pump, wherein said transfer box extends from said housing and through said hull.
 17. The water jet propulsion system of claim 16, further comprising a gear set for transferring rotation from said prime mover to said pump.
 18. The water jet propulsion system of claim 15, further comprising an inlet opening, a discharge opening and wherein said inlet opening, discharge opening and pump are arranged along a common longitudinal axis.
 19. The water jet propulsion system of claim 15, wherein said outlet orifice has a variable cross-sectional area.
 20. The water jet propulsion system of claim 15, wherein said lobe pump is reversible so as to enable water to be pumped from said outlet opening to said inlet opening and thereby enable a reversing of said watercraft. 